1. Field of the Invention
The present invention relates to an image recognition apparatus for calculating the distance to a target object based on a binocular stereovision image obtained using two imaging devices.
2. Description of the Related Art
Conventionally, in order to notify the driver of a vehicle about an obstacle such as a pedestrian in its path, devices in which images taken by one or a plurality of cameras mounted on the front of the vehicle are displayed at a position visible from the driver's seat to complement the forward visibility of the driver, and devices which detect obstacles which may contact the vehicle based on the images taken by the cameras, and cause the vehicle to perform automatic avoidance operations, are already known. The image displayed to the driver is displayed on an image display apparatus such as a NAVIDisplay positioned in the console of the vehicle, a HUD (Head Up Display) which displays information at a position on the front window which does not obscure the forward visibility of the driver, or a meter integrated display which is integrated with a meter which displays the travel state of the vehicle numerically. Furthermore, the automatic avoidance operations of the vehicle are performed by automatically controlling a variety of actuators which are provided to operate each section of the vehicle.
An example of this type of apparatus in which an image is taken of the environment in the vicinity of the vehicle, and obstacles which may contact the vehicle are detected from the captured image, is disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 6-266828. In this apparatus, the images taken by two cameras are processed, and information on the distance distribution across the entire image is obtained, and by then calculating three dimensional positional information of target objects corresponding with the distance distribution information, the shape of the road and obstacles such as side walls are easily and accurately detected. Consequently, it is possible to individually recognize the presence of a plurality of obstacles, and either warn the driver of the vehicle, or have the vehicle perform automatic avoidance operations with a high degree of reliability.
However, conventional apparatuses such as those described above have a problem in that, when determining the distance distribution across the entire image, because the entire image is divided into regions of a certain size and the distance distribution is calculated for each region, the size of the region relative to the size of the target object is fixed, and the processing efficiency is thus poor.
In other words, when the captured image of a target object occupies a large proportion of the entire image, because only a single distance to the target object need be obtained, if the target object is divided up more than necessary and the distance distribution for each region is determined, the efficiency of the processing is poor, and considerable time is required for the entire distance distribution to be calculated in order to calculate the distance to the target object.